title: Uranium association with iron-bearing phases in mill tailings from Gunnar, Canada.
abstract: The speciation of uranium was studied in the mill tailings of the Gunnar uranium mine (Saskatchewan, Canada), which operated in the 1950s and 1960s. The nature, quantification, and spatial distribution of uranium-bearing phases were investigated by chemical and mineralogical analyses, fission track mapping, electron microscopy, and X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopies at the U LIII-edge and Fe K-edge. In addition to uranium-containing phases from the ore, uranium is mostly associated with iron-bearing minerals in all tailing sites. XANES and EXAFS data and transmission electron microscopy analyses of the samples with the highest uranium concentrations (∼400-700 mg kg(-1) of U) demonstrate that uranium primarily occurs as monomeric uranyl ions (UO2(2+)), forming inner-sphere surface complexes bound to ferrihydrite (50-70% of the total U) and to a lesser extent to chlorite (30-40% of the total U). Thus, the stability and mobility of uranium at the Gunnar site are mainly influenced by sorption/desorption processes. In this context, acidic pH or alkaline pH with the presence of UO2(2+)- and/or Fe(3+)-complexing agents (e.g., carbonate) could potentially solubilize U in the tailings pore waters.
authors.affiliation: Institut de Minéralogie et de Physique des Milieux Condensés (IMPMC), UMR 7590 CNRS-UPMC/Paris VI-IRD, Case 115 , 4 place Jussieu, 75252 Paris Cedex 05, France.
authors.forename: Guillaume
authors.initials: G
authors.lastname: Othmane
authors.forename: Thierry
authors.initials: T
authors.lastname: Allard
authors.forename: Guillaume
authors.initials: G
authors.lastname: Morin
authors.forename: Madeleine
authors.initials: M
authors.lastname: Sélo
authors.forename: Jessica
authors.initials: J
authors.lastname: Brest
authors.forename: Isabelle
authors.initials: I
authors.lastname: Llorens
authors.forename: Ning
authors.initials: N
authors.lastname: Chen
authors.forename: John R
authors.initials: JR
authors.lastname: Bargar
authors.forename: Mostafa
authors.initials: M
authors.lastname: Fayek
authors.forename: Georges
authors.initials: G
authors.lastname: Calas
mesh_terms: D002170:Canada; D005583:Fourier Analysis; D007501:Iron / Q000737:chemistry*; D008855:Microscopy, Electron, Scanning; D008903:Minerals / Q000032:analysis; D008906:Mining; D014501:Uranium / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*; D056928:X-Ray Absorption Spectroscopy
chemical_list: D008903:Minerals; D014874:Water Pollutants, Chemical; D014501:Uranium; D007501:Iron